There are many chemical and petroleum processes in which solid particles of fluidizable size are suspended in a gas during reaction conditions. One example of such processes is the fluidized catalytic cracking of petroleum. In this process, a petroleum feedstock is contacted with a solid catalyst at temperatures in the range of about 480.degree. C. to about 800.degree. C. In the past, the catalyst particles in a fluidized catalytic cracking process were maintained in a reactor in a dense fluidized state or bed. More recently, the trend has been to conduct fluidized catalytic cracking of petroleum without the maintenance of a dense fluidized bed of catalyst particles. Instead, the solid catalyst is suspended as a dilute phase in a fluid which is passed through the reactor vessel at sufficiently high velocities so that the reactants pass rapidly through the hydrocarbon conversion zone. This procedure reduces the residence time of the reactants in the hydrocarbon conversion zone to a predetermined time which is a function of catalyst activity, temperature, nature of the feed and the like. In effect, it permits use of higher activity catalyst and higher temperatures than previously practical.
In all of these processes, fluid reactors, regenerators and similar vessels must be provided with means for separating the solid particles from the gaseous phase. Typically, this is accomplished by cyclones located in the upper part of the vessel. The solids separate from the gaseous fluid in this cyclone are returned to the fluid solids contacting zone by the cyclone dipleg.
For cyclones to operate efficiently, it is necessary to prevent the ingress of fluidizing gas into the dipleg of the cyclone. Trickle valves have been used for this purpose. Basically, these consist of an angularly oriented conduit having one end operably connected to the dipleg of the cyclone and a hinged flapper or closure plate at the opposite end for opening and closing the conduit. Examples of these trickle valves can be found in U.S. Pat. Nos. 2,838,062; 2,838,065; 2,901,331; 3,698,874; 4,246,231; and 4,446,107.
These references evidence the fact that satisfactory operation of trickle valves has always been a problem. Recent experience, moreover, has shown that achieving satisfactory performance of trickle valves in dilute phase fluid solids contacting zones is even more difficult. Thus, it is an object of the present invention to provide an improved trickle valve. Indeed, it is an object of the present invention to provide an improved trickle valve suitable especially for use in fluid solids contacting zones, particularly dilute phase fluid solids contacting zones.